1. Field of the Invention
The invention relates to a magnetostrictive torque sensor.
2. Description of the Related Art
Known magnetostrictive torque sensors are provided with a rotating shaft having a magnetostrictive characteristic that a magnetic permeability varies according to an applied torque, and a detection coil, wherein the detection coil can detect a variation in magnetic permeability of the rotating shaft under the applied torque as a variation in inductance thereof, thereby detecting a torque (rotation torque) applied to the rotating shaft.
When a torque is applied to the rotating shaft, a compressive (or tensile) stress acts in a direction inclined at +45 degrees relative to an axial direction and a tensile (or compressive) stress acts in a direction inclined at −45 degrees relative to the axial direction. Thus, the torque sensor is configured such that variations in magnetic permeability in the directions inclined at +45 degrees and −45 degrees relative to the axial direction are respectively detected by two detection coils and a difference in voltage between two ends is measured on the both detection coils by using a bridge circuit etc., whereby the torque applied to the rotating shaft can be detected at high sensitivity.
A magnetostrictive torque sensor is disclosed in JP-B-4,888,015.
JP-B-4,888,015 proposes a substrate-coil type torque sensor in which a detection coil is formed using a wiring pattern formed on a flexible circuit board so as to have a side inclined at +45 degrees relative to the axial direction of the rotating shaft and a side inclined at −45 degrees and the flexible circuit board is attached to an inner peripheral surface of a magnetic ring.